1. Field of Invention
The present invention relates to an optical packet routing system for routing an optical signal by using the optical label signal carrying the control information necessary for the routing of the optical signal, more particularly, to a multiple-wavelength optical source unit to be used for a network system whose a plurality of communication nodes are connected by the wavelength routing system and an optical communication unit and an optical communication method to be used for an optical communication system whose internode communication among the communication nodes is made through a routing unit.
2. Description of the Art
With the explosive spread of the internets, and portable personal telephones and the like, the research and development activities for the establishment of large-capacity network are under way both at home and abroad. With the communication nodes constituting each of the existing networks, an optical signal transmitted through an optical fiber transmission line is converted into an electric signal; an address information and the like carried by the signal is read out; the signal is electrically switched to a desired output port according to the information; the signal is converted into an optical signal at the output port; and the optical signal is then transmitted through the optical fiber transmission line. However, with the exponential-growth in the communication traffic, in the near future, the routing processing capacity by the electrical routing processes is considered to reach its limit. To overcome this problem, it is important for the communication nodes to establish a routing method for enabling the routing of the signal within the optical layer, that is, a routing method for enabling the routing without converting the optical signal into the electric signal.
As a technique for realizing the above goal, the wavelength routing technique is coming to the fore. In the case of the wavelength routing technique as schematically illustrated in FIG. 1, any optical signal fed into a given input port can be routed selectively to different output ports according to its wavelength without being converted into an electric signal, by using an optical device (e.g., arrayed-waveguide grating) having a wavelength selectivity.
FIG. 2 schematically illustrates the general composition of the network system interconnecting a plurality of communication nodes by utilizing the wavelength routing function of the cyclic-wavelength arrayed-waveguide grating. In the case of this network system, with a cyclic-wavelength arrayed-waveguide grating 60 having a wavelength routing processing function, the optical signal transmitted from a communication node is routed in the form of the light according to its wavelength without undergoing any electrical processing for routing, so that high-speed routing is possible.
To illustrate the composition of FIG. 2, the network system comprises N number of communication nodes 30 (communication nodes #1–N) and a cyclic-wavelength arrayed-waveguide grating 60 having a wavelength routing processing function. Each communication node 30 comprises transmitter equipment 40 and receiver equipment 50. The transmitter equipment 40 comprises N number of optical sources 41 for transmitting optical signals having wavelengths λ1–λn.
The optical signals (wavelength: λ1–λn) transmitted from the transmitter equipment 40 of each communication node 30 are introduced into the input ports of the cyclic-wavelength arrayed-waveguide grating 60 having the wavelength routing processing function. The cyclic-wavelength arrayed-waveguide grating 60 routes the optical signals incoming from various communication nodes 30 to different output ports according to the wavelengths, λ1–λn , of the optical signals. Since this routing processing of the optical signal is carried out according to the wavelength of the optical signal while maintaining the form of the light without being subjected to any electrical processing, the high-speed routing is possible.
The optical signals (wavelength: λ1–λn) came out from the output ports of the cyclic-wavelength arrayed-waveguide grating 60 is introduced into the receiver equipment 50 in each communication node 30.
The detail of the wavelength routing processing by the cyclic-wavelength arrayed-waveguide grating 60 will be described referring to FIG. 3. Optical signals (wavelength: λ1–λ4) varying in wavelength transmitted from various communication nodes (#1–#4) are fed to the input ports 61a–61d of the cyclic-wavelength arrayed-waveguide grating 60. In this case, the optical signal transmitted from the communication node #1 to the input node 61a is outputted from the output port 62a when its wavelength is λ1, from the output port 62b when its wavelength is λ2, from the output port 62c when the wavelength is λ3 and from 62d when the wavelength is λ4.
The optical signal to be transmitted from the communication node #2 to the input port 61b is outputted from the output port 62d when its wavelength is λ1, from the output port 62a when its wavelength is λ2, from the output port 62b when its wavelength is λ3, and from the output port 62c when its wavelength is λ4.
The optical signal to be transmitted from the communication node #3 is outputted from the output port 62c when its wavelength is λ1, from the output port 62d when its wavelength is λ2, and from the output port 62a when its wavelength is λ3, and from the output port 62b when its wavelength is λ4.
The optical signal to be transmitted from the communication node #4 to the input port 61d is outputted from the output port 62b when its wavelength is λ1, from the output port 62c when its wavelength is λ2, from the output port 62d when its wavelength is λ3, and from the output port 62a when its wavelength is λ4.
Thus, by the routing to be carried out as described above, the optical signals having the same wavelengths respectively transmitted from the communication nodes #1–#4 will never be outputted from the same output port. In other words, the wavelength routing by using the cyclic-wavelength arrayed-waveguide grating as is shown in FIG. 3 is characterized by that the optical signals having the same wavelengths fed to different input ports of the grating are outputted from different output ports of the grating respectively, so that the conflict among the data having the same wavelengths with respect to the output port can be prevented.
However, in the case of conventional network system as is shown in FIG. 2, especially in the case of the network comprising N number of communication nodes, it is necessary to provide N number of optical sources with wavelengths strictly adapted to the wavelength characteristic of the cyclic-wavelength arrayed-waveguide grating with respect to each of the communication nodes and thus requiring N×N number of optical sources, which is a problem to be resolved. Especially, providing N number of optical sources for each communication node not only results in the increase in the burdens such as the increase in the size and cost of the communication node but also results in the increase in total cost of the network system.
Next, a prior art relating to the second embodiment of the present invention will be described.
Conventionally, as an optical communication system for carrying out the optical communication among a plurality of communication nodes through a router, a system shown in FIG. 4 has been available.
The communication nodes 100a–100d are respectively provided with one of the corresponding optical signal transmitters 71a–71d for respectively transmitting one of the corresponding optical signals 76a–76d and also respectively provided with one of the corresponding optical label signal transmitters 72a–72d for respectively transmitting one of the corresponding optical label signals 77a–77d carrying the control information necessary for the routing of the optical signal.
The routing device 80 is connected respectively to each communication nodes 100a–100d through the corresponding optical transmission lines 81a–81d and comprises wavelength demultiplexers 74 for separating the optical signals and the optical label signals, optical receivers 78e for receiving the optical label signals separated by the wavelength multiplexers 74, optical splitters 79 for branching the optical signals separated by the wavelength demultiplexers 74 to a plurality of optical paths and a plurality of optical gates 75a–75d for selecting the optical path by the routing processing for passing or intercepting the optical signals according to the control information in the optical label signals 77a–77d respectively connected to a plurality of the corresponding optical paths. The control circuit section for controlling the optical gates 75a–75d are not shown in the figure.
When the optical signals 76a–76d and the optical label signals 77a–77d respectively including the control routing information of the optical signals are fed respectively to the router 80 through the optical transmission lines 81a–81d after being transmitted respectively from a plurality of communication nodes 100a–100d (the four communication nodes #1–#4 in the case shown in the figure), the optical signals 76a–76d and the optical label signals 77a–77d are respectively separated by the wavelength demultiplexers 74 provided in the router 80 respectively corresponding to the communication nodes.
Further, the optical signals 76a–76d are respectively branched by the optical splitter 79 in the stage following the wavelength demultiplexer 74 and respectively introduced into the corresponding optical gates (three optical gates among the optical gates 75a–75d in the case shown in the figure) through a plurality of optical paths of substantially the same length (three optical paths in the case shown in the figure). On the other hand, the optical label signals 77a–77d are respectively guided to the corresponding optical receivers 78e. Next, when the optical signal passes one or a plurality of optical gates among a plurality of optical gates 75a–75d, which is or are designed to be driven according to the information carried by the optical label signal received by the optical receiver 78e, the optical path for the optical signal is selected from among the optical paths 82a–82d. 
The time required for the optical signal 76 (the representative number of 76a–76d) to arrive at the optical gate 75 (the representative number of 75a–75d) from the input port of the wavelength demultiplexer 74 of the router 80 is given as t1; the time required for the optical label signal 77 (the representative number of 77a–77d) corresponding to the optical signal 76 to arrive at the optical receiver 78e from the input port of the wavelength demultiplexer 74 is given as t2; the time required for the optical receiver 78e to drive the optical gate 75 (to permit the optical signal to pass) after completing the reception of the optical label signal 77. Under these conditions, in the optical gate 75, in order for the optical signal 76 to be processed for proper gating, it is necessary for each of the communication nodes 100 (the representative number of 100a–100d) to output both the optical signal 76 and the optical label signal 77 respectively with a time lag so that the time lag becomes equal to the relative time lag T′ (the time lag between the front of the optical signal 76 and the end of optical label signal 77 arrived at the input port of the wavelength demultiplexer 74, denoted by numeral 90 in FIG. 5) to satisfy the inequality (1) given below.T′>t2+t3−t1  (1)
On the other hand, in order to raise the data communication efficiency among the communication nodes 100, as shown in FIG. 6, it is necessary to adjust the relative time lag T′ in the above inequality (1) so that the time lag Δt (denoted by numeral 91) between the arrival time of the optical signal 76 at the optical gates 75 to drive the optical gates 75 and the time (denoted by numeral 92) at which the optical signal is allowed to pass is reduced as far as possible.
By predetermining the values of t1, t2 and t3 in the above inequality (1), the relative time lag T′ between the optical signal 76 and the optical label signal 77, which is necessary for proper gating of the optical signal 76 by the optical gate 75, can be determined.
However, in general, in the case of the optical communication system by using the optical label signal, for the easy separation of the optical signal and the optical label signal by the router 80, these signals have different wavelengths. Therefore, the relative time lag between the optical signal and the optical label signal varies according to transmission distance due to the effect of the wavelength dispersion of the optical fiber which is a transmission medium of the optical signal. In consequence, the time lag T between the transmission of the optical signal and that of the optical label signal set by the communication node 100 differs from the relative time lag T′ at immediately before the input port of the wavelength demultiplexer 74 of the router 80. Since the distances from various communication nodes 100 to the router 80 vary, it is necessary to adjust the transmission time lag T between the transmission of the optical signal and that of the optical label signal so that the relative time lag T′ for each of the communication nodes 100 satisfies the above inequality (1).
However, since the router and each communication node are, in general, arranged at physically separated locations, when setting the previously mentioned transmission time lag T at each communication node, it is necessary to adjust in real-time conjunction so that the data is transmitted properly to each communication node, but this process is very cumbersome in the case of the conventional system.